Application-layer handoff of an access terminal from a first system of an access network to a second system of the access network during a communication session within a wireless communications system

ABSTRACT

Embodiments are directed to an application-layer handoff of an access terminal from a first system of an access network to a second system of the access network during a communication session within a wireless communications system. In an embodiment, the access terminal sets up a communication session on the first system. A multimedia client measures application-layer performance parameters for the communication session supported by the first system, and determines whether to handoff the communication session to a second system based at least in part on the application-layer performance parameters. If the multimedia client determines to handoff the communication session to the second system, the multimedia client initiates the handoff and the communication session is transitioned to the second system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention are directed to anapplication-layer handoff of an access terminal from a first system ofan access network to a second system of the access network during acommunication session within a wireless communications system.

2. Description of the Related Art

Wireless communication systems have developed through variousgenerations, including a first-generation analog wireless phone service(1G), a second-generation (2G) digital wireless phone service (includinginterim 2.5G and 2.75G networks) and a third-generation (3G) high speeddata/Internet-capable wireless service. There are presently manydifferent types of wireless communication systems in use, includingCellular and Personal Communications Service (PCS) systems. Examples ofknown cellular systems include the cellular Analog Advanced Mobile PhoneSystem (AMPS), and digital cellular systems based on Code DivisionMultiple Access (CDMA), Frequency Division Multiple Access (FDMA), TimeDivision Multiple Access (TDMA), the Global System for Mobile access(GSM) variation of TDMA, and newer hybrid digital communication systemsusing both TDMA and CDMA technologies.

The method for providing CDMA mobile communications was standardized inthe United States by the Telecommunications IndustryAssociation/Electronic Industries Association in TIA/EIA/IS-95-Aentitled “Mobile Station-Base Station Compatibility Standard forDual-Mode Wideband Spread Spectrum Cellular System,” referred to hereinas IS-95. Combined AMPS & CDMA systems are described in TIA/EIA StandardIS-98. Other communications systems are described in the IMT-2000/UM, orInternational Mobile Telecommunications System 2000/Universal MobileTelecommunications System, standards covering what are referred to aswideband CDMA (WCDMA), CDMA2000 (such as CDMA2000 1xEV-DO standards, forexample) or TD-SCDMA.

In wireless communication systems, mobile stations, handsets, or accessterminals (AT) receive signals from fixed position base stations (alsoreferred to as cell sites or cells) that support communication links orservice within particular geographic regions adjacent to or surroundingthe base stations. Base stations provide entry points to an accessnetwork (AN)/radio access network (RAN), which is generally a packetdata network using standard Internet Engineering Task Force (IETF) basedprotocols that support methods for differentiating traffic based onQuality of Service (QoS) requirements. Therefore, the base stationsgenerally interact with ATs through an over the air interface and withthe AN through Internet Protocol (IP) network data packets.

In wireless telecommunication systems, Push-to-talk (PTT) capabilitiesare becoming popular with service sectors and consumers. PTT can supporta “dispatch” voice service that operates over standard commercialwireless infrastructures, such as CDMA, FDMA, TDMA, GSM, etc. In adispatch model, communication between endpoints (ATs) occurs withinvirtual groups, wherein the voice of one “talker” is transmitted to oneor more “listeners.” A single instance of this type of communication iscommonly referred to as a dispatch call, or simply a PTT call. A PTTcall is an instantiation of a group, which defines the characteristicsof a call. A group in essence is defined by a member list and associatedinformation, such as group name or group identification.

Conventionally, data packets within a wireless communications networkhave been configured to be sent to a single destination or accessterminal. A transmission of data to a single destination is referred toas “unicast”. As mobile communications have increased, the ability totransmit given data concurrently to multiple access terminals has becomemore important. Accordingly, protocols have been adopted to supportconcurrent data transmissions of the same packet or message to multipledestinations or target access terminals. A “broadcast” refers to atransmission of data packets to all destinations or access terminals(e.g., within a given cell, served by a given service provider, etc.),while a “multicast” refers to a transmission of data packets to a givengroup of destinations or access terminals. In an example, the givengroup of destinations or “multicast group” may include more than one andless than all of possible destinations or access terminals (e.g., withina given group, served by a given service provider, etc.). However, it isat least possible in certain situations that the multicast groupcomprises only one access terminal, similar to a unicast, oralternatively that the multicast group comprises all access terminals(e.g., within a cell or sector), similar to a broadcast.

Broadcasts and/or multicasts may be performed within wirelesscommunication systems in a number of ways, such as performing aplurality of sequential unicast operations to accommodate the multicastgroup, allocating a unique broadcast/multicast channel (BCH) forhandling multiple data transmissions at the same time and the like. Aconventional system using a broadcast channel for push-to-talkcommunications is described in United States Patent ApplicationPublication No. 2007/0049314 dated Mar. 1, 2007 and entitled“Push-To-Talk Group Call System Using CDMA 1x-EVDO Cellular Network”,the contents of which are incorporated herein by reference in itsentirety. As described in Publication No. 2007/0049314, a broadcastchannel can be used for push-to-talk calls using conventional signalingtechniques. Although the use of a broadcast channel may improvebandwidth requirements over conventional unicast techniques, theconventional signaling of the broadcast channel can still result inadditional overhead and/or delay and may degrade system performance.

The 3^(rd) Generation Partnership Project 2 (“3GPP2”) defines abroadcast-multicast service (BCMCS) specification for supportingmulticast communications in CDMA2000 networks. Accordingly, a version of3GPP2's BCMCS specification, entitled “CDMA2000 High RateBroadcast-Multicast Packet Data Air Interface Specification”, dated Feb.14, 2006, Version 1.0 C.S0054-A, is hereby incorporated by reference inits entirety.

SUMMARY

Embodiments are directed to an application-layer handoff of an accessterminal from a first system of an access network to a second system ofthe access network during a communication session within a wirelesscommunications system. In an embodiment, the access terminal sets up acommunication session on the first system. A multimedia client measuresapplication-layer performance parameters for the communication sessionsupported by the first system, and determines whether to handoff thecommunication session to a second system based at least in part on theapplication-layer performance parameters. If the multimedia clientdetermines to handoff the communication session to the second system,the multimedia client initiates the handoff and the communicationsession is transitioned to the second system.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the invention and many ofthe attendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingswhich are presented solely for illustration and not limitation of theinvention, and in which:

FIG. 1 is a diagram of a wireless network architecture that supportsaccess terminals and access networks in accordance with at least oneembodiment of the invention.

FIG. 2A illustrates the core network of FIG. 1 according to anembodiment of the present invention.

FIG. 2B illustrates an example of the wireless communications system ofFIG. 1 in more detail.

FIG. 3 is an illustration of an access terminal in accordance with atleast one embodiment of the invention.

FIG. 4 illustrates a conventional inter-system handoff of a given accessterminal that is participating in a wireless communication session.

FIG. 5 illustrates a system-handoff of a given access terminal that isparticipating in a wireless communication session in accordance with anembodiment of the invention.

FIG. 6A illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to a location of thegiven access terminal within the wireless communications system inaccordance with an embodiment of the invention.

FIG. 6B illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to a media errorrate (MER) for the given access terminal's communication session withinthe wireless communications system in accordance with an embodiment ofthe invention.

FIG. 6C illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to an outageduration for the given access terminal's communication session withinthe wireless communications system in accordance with an embodiment ofthe invention.

FIG. 6D illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to a current rate atwhich a subscriber using the given access terminal is being charged forservice related to the given access terminal's communication sessionwithin the wireless communications system in accordance with anembodiment of the invention.

FIG. 6E illustrates the system-handoff process of FIG. 5 whereby one ormore application-layer performance parameters are considered during apotential handoff of the given access terminal from a first system toone of a plurality of other potential systems during the given accessterminal's communication session within the wireless communicationssystem in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the scope ofthe invention. Additionally, well-known elements of the invention willnot be described in detail or will be omitted so as not to obscure therelevant details of the invention.

The words “exemplary” and/or “example” are used herein to mean “servingas an example, instance, or illustration.” Any embodiment describedherein as “exemplary” and/or “example” is not necessarily to beconstrued as preferred or advantageous over other embodiments. Likewise,the term “embodiments of the invention” does not require that allembodiments of the invention include the discussed feature, advantage ormode of operation.

Further, many embodiments are described in terms of sequences of actionsto be performed by, for example, elements of a computing device. It willbe recognized that various actions described herein can be performed byspecific circuits (e.g., application specific integrated circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. Additionally, these sequence ofactions described herein can be considered to be embodied entirelywithin any form of computer readable storage medium having storedtherein a corresponding set of computer instructions that upon executionwould cause an associated processor to perform the functionalitydescribed herein. Thus, the various aspects of the invention may beembodied in a number of different forms, all of which have beencontemplated to be within the scope of the claimed subject matter. Inaddition, for each of the embodiments described herein, thecorresponding form of any such embodiments may be described herein as,for example, “logic configured to” perform the described action.

A High Data Rate (HDR) subscriber station, referred to herein as anaccess terminal (AT), may be mobile or stationary, and may communicatewith one or more HDR base stations, referred to herein as modem pooltransceivers (MPTs) or base stations (BS). An access terminal transmitsand receives data packets through one or more modem pool transceivers toan HDR base station controller, referred to as a modem pool controller(MPC), base station controller (BSC) and/or packet control function(PCF). Modem pool transceivers and modem pool controllers are parts of anetwork called an access network. An access network transports datapackets between multiple access terminals.

The access network may be further connected to additional networksoutside the access network, such as a corporate intranet or theInternet, and may transport data packets between each access terminaland such outside networks. An access terminal that has established anactive traffic channel connection with one or more modem pooltransceivers is called an active access terminal, and is said to be in atraffic state. An access terminal that is in the process of establishingan active traffic channel connection with one or more modem pooltransceivers is said to be in a connection setup state. An accessterminal may be any data device that communicates through a wirelesschannel or through a wired channel, for example using fiber optic orcoaxial cables. An access terminal may further be any of a number oftypes of devices including but not limited to PC card, compact flash,external or internal modem, or wireless or wireline phone. Thecommunication link through which the access terminal sends signals tothe modem pool transceiver is called a reverse link or traffic channel.The communication link through which a modem pool transceiver sendssignals to an access terminal is called a forward link or trafficchannel. As used herein the term traffic channel can refer to either aforward or reverse traffic channel.

FIG. 1 illustrates a block diagram of one exemplary embodiment of awireless system 100 in accordance with at least one embodiment of theinvention. System 100 can contain access terminals, such as cellulartelephone 102, in communication across an air interface 104 with anaccess network or radio access network (RAN) 120 that can connect theaccess terminal 102 to network equipment providing data connectivitybetween a packet switched data network (e.g., an intranet, the Internet,and/or carrier network 126) and the access terminals 102, 108, 110, 112.As shown here, the access terminal can be a cellular telephone 102, apersonal digital assistant 108, a pager 110, which is shown here as atwo-way text pager, or even a separate computer platform 112 that has awireless communication portal. Embodiments of the invention can thus berealized on any form of access terminal including a wirelesscommunication portal or having wireless communication capabilities,including without limitation, wireless modems, PCMCIA cards, personalcomputers, telephones, or any combination or sub-combination thereof.Further, as used herein, the terms “access terminal”, “wireless device”,“client device”, “mobile terminal” and variations thereof may be usedinterchangeably.

Referring back to FIG. 1, the components of the wireless network 100 andinterrelation of the elements of the exemplary embodiments of theinvention are not limited to the configuration illustrated. System 100is merely exemplary and can include any system that allows remote accessterminals, such as wireless client computing devices 102, 108, 110, 112to communicate over-the-air between and among each other and/or betweenand among components connected via the air interface 104 and RAN 120,including, without limitation, carrier network 126, the Internet, and/orother remote servers.

The RAN 120 controls messages (typically sent as data packets) sent to abase station controller/packet control function (BSC/PCF) 122. TheBSC/PCF 122 is responsible for signaling, establishing, and tearing downbearer channels (i.e., data channels) between a packet data service node100 (“PDSN”) and the access terminals 102/108/110/112. If link layerencryption is enabled, the BSC/PCF 122 also encrypts the content beforeforwarding it over the air interface 104. The function of the BSC/PCF122 is well-known in the art and will not be discussed further for thesake of brevity. The carrier network 126 may communicate with theBSC/PCF 122 by a network, the Internet and/or a public switchedtelephone network (PSTN). Alternatively, the BSC/PCF 122 may connectdirectly to the Internet or external network. Typically, the network orInternet connection between the carrier network 126 and the BSC/PCF 122transfers data, and the PSTN transfers voice information. The BSC/PCF122 can be connected to multiple base stations (BS) or modem pooltransceivers (MPT) 124. In a similar manner to the carrier network, theBSC/PCF 122 is typically connected to the MPT/BS 124 by a network, theInternet and/or PSTN for data transfer and/or voice information. TheMPT/BS 124 can broadcast data messages wirelessly to the accessterminals, such as cellular telephone 102. The MPT/BS 124, BSC/PCF 122and other components may form the RAN 120, as is known in the art.However, alternate configurations may also be used and the invention isnot limited to the configuration illustrated. For example, in anotherembodiment the functionality of the BSC/PCF 122 and one or more of theMPT/BS 124 may be collapsed into a single “hybrid” module having thefunctionality of both the BSC/PCF 122 and the MPT/BS 124.

FIG. 2A illustrates the carrier network 126 according to an embodimentof the present invention. In the embodiment of FIG. 2A, the carriernetwork 126 includes a packet data serving node (PDSN) 160, a broadcastserving node (BSN) 165, an application server 170 and an Internet 175.However, application server 170 and other components may be locatedoutside the carrier network in alternative embodiments. The PDSN 160provides access to the Internet 175, intranets and/or remote servers(e.g., application server 170) for mobile stations (e.g., accessterminals, such as 102, 108, 110, 112 from FIG. 1) utilizing, forexample, a cdma2000 Radio Access Network (RAN) (e.g., RAN 120 of FIG.1). Acting as an access gateway, the PDSN 160 may provide simple IP andmobile IP access, foreign agent support, and packet transport. The PDSN160 can act as a client for Authentication, Authorization, andAccounting (AAA) servers and other supporting infrastructure andprovides mobile stations with a gateway to the IP network as is known inthe art. As shown in FIG. 2A, the PDSN 160 may communicate with the RAN120 (e.g., the BSC/PCF 122) via a conventional A10 connection. The A10connection is well-known in the art and will not be described furtherfor the sake of brevity.

Referring to FIG. 2A, the broadcast serving node (BSN) 165 may beconfigured to support multicast and broadcast services. The BSN 165 willbe described in greater detail below. The BSN 165 communicates with theRAN 120 (e.g., the BSC/PCF 122) via a broadcast (BC) A10 connection, andwith the application server 170 via the Internet 175. The BCA10connection is used to transfer multicast and/or broadcast messaging.Accordingly, the application server 170 sends unicast messaging to thePDSN 160 via the Internet 175, and sends multicast messaging to the BSN165 via the Internet 175.

Generally, as will be described in greater detail below, the RAN 120transmits multicast messages, received from the BSN 165 via the BCA10connection, over a broadcast channel (BCH) of the air interface 104 toone or more access terminals 200.

FIG. 2B illustrates an example of the wireless communication 100 of FIG.1 in more detail. In particular, referring to FIG. 2B, ATs 1 . . . N areshown as connecting to the RAN 120 at locations serviced by differentpacket data network end-points. Accordingly, ATs 1 and 3 connect to theRAN 120 at a portion served by a first packet data network end-point 162(e.g., which may correspond to PDSN 160, BSN 165, a home agent (HA), aforeign agent (FA), etc.). The first packet data network end-point 162in turn connects, via the routing unit 188, to the Internet 175 and/orto one or more of an authentication, authorization and accounting (AAA)server 182, a provisioning server 184, an Internet Protocol (IP)Multimedia Subsystem (IMS)/Session Initiation Protocol (SIP)Registration Server 186 and/or the application server 170. ATs 2 and 5 .. . N connect to the RAN 120 at a portion served by a second packet datanetwork end-point 164 (e.g., which may correspond to PDSN 160, BSN 165,FA, HA, etc.). Similar to the first packet data network end-point 162,the second packet data network end-point 164 in turn connects, via therouting unit 188, to the Internet 175 and/or to one or more of the AAAserver 182, a provisioning server 184, an IMS/SIP Registration Server186 and/or the application server 170. AT 4 connects directly to theInternet 175, and through the Internet 175 can then connect to any ofthe system components described above.

Referring to FIG. 2B, ATs 1, 3 and 5 . . . N are illustrated as wirelesscell-phones, AT 2 is illustrated as a wireless tablet-PC and AT 4 isillustrated as a wired desktop station. However, in other embodiments,it will be appreciated that the wireless communication system 100 canconnect to any type of AT, and the examples illustrated in FIG. 2B arenot intended to limit the types of ATs that may be implemented withinthe system. Also, while the AAA 182, the provisioning server 184, theIMS/SIP registration server 186 and the application server 170 are eachillustrated as structurally separate servers, one or more of theseservers may be consolidated in at least one embodiment of the invention.

Further, referring to FIG. 2B, the application server 170 is illustratedas including a plurality of media control complexes (MCCs) 1 . . . N170B, and a plurality of regional dispatchers 1 . . . N 170A.Collectively, the regional dispatchers 170A and MCCs 170B are includedwithin the application server 170, which in at least one embodiment cancorrespond to a distributed network of servers that collectivelyfunctions to arbitrate communication sessions (e.g., half-duplex groupcommunication sessions via IP unicasting and/or IP multicastingprotocols) within the wireless communication system 100. For example,because the communication sessions arbitrated by the application server170 can theoretically take place between ATs located anywhere within thesystem 100, multiple regional dispatchers 170A and MCCs are distributedto reduce latency for the arbitrated communication sessions (e.g., sothat a MCC in North America is not relaying media back-and-forth betweensession participants located in China). Thus, when reference is made tothe application server 170, it will be appreciated that the associatedfunctionality can be enforced by one or more of the regional dispatchers170A and/or one or more of the MCCs 170B. The regional dispatchers 170Aare generally responsible for any functionality related to establishinga communication session (e.g., handling signaling messages between theATs, scheduling and/or sending announce messages, etc.), whereas theMCCs 170B are responsible for hosting the communication session for theduration of the call instance, including conducting an in-call signalingand an actual exchange of media during an arbitrated communicationsession.

Referring to FIG. 3, an access terminal 200, (here a wireless device),such as a cellular telephone, has a platform 202 that can receive andexecute software applications, data and/or commands transmitted from theRAN 120 that may ultimately come from the carrier network 126, theInternet and/or other remote servers and networks. The platform 202 caninclude a transceiver 206 operably coupled to an application specificintegrated circuit (“ASIC” 208), or other processor, microprocessor,logic circuit, or other data processing device. The ASIC 208 or otherprocessor executes the application programming interface (“API”) 210layer that interfaces with any resident programs in the memory 212 ofthe wireless device. The memory 212 can be comprised of read-only orrandom-access memory (RAM and ROM), EEPROM, flash cards, or any memorycommon to computer platforms. The platform 202 also can include a localdatabase 214 that can hold applications not actively used in memory 212.The local database 214 is typically a flash memory cell, but can be anysecondary storage device as known in the art, such as magnetic media,EEPROM, optical media, tape, soft or hard disk, or the like. Theinternal platform 202 components can also be operably coupled toexternal devices such as antenna 222, display 224, push-to-talk button228 and keypad 226 among other components, as is known in the art.

Accordingly, an embodiment of the invention can include an accessterminal including the ability to perform the functions describedherein. As will be appreciated by those skilled in the art, the variouslogic elements can be embodied in discrete elements, software modulesexecuted on a processor or any combination of software and hardware toachieve the functionality disclosed herein. For example, ASIC 208,memory 212, API 210 and local database 214 may all be used cooperativelyto load, store and execute the various functions disclosed herein andthus the logic to perform these functions may be distributed overvarious elements. Alternatively, the functionality could be incorporatedinto one discrete component. Therefore, the features of the accessterminal in FIG. 3 are to be considered merely illustrative and theinvention is not limited to the illustrated features or arrangement.

The wireless communication between the access terminal 102 and the RAN120 can be based on different technologies, such as code divisionmultiple access (CDMA), WCDMA, time division multiple access (TDMA),frequency division multiple access (FDMA), Orthogonal Frequency DivisionMultiplexing (OFDM), the Global System for Mobile Communications (GSM),or other protocols that may be used in a wireless communications networkor a data communications network. The data communication is typicallybetween the client device 102, MPT/BS 124, and BSC/PCF 122. The BSC/PCF122 can be connected to multiple data networks such as the carriernetwork 126, PSTN, the Internet, a virtual private network, and thelike, thus allowing the access terminal 102 access to a broadercommunication network. As discussed in the foregoing and known in theart, voice transmission and/or data can be transmitted to the accessterminals from the RAN using a variety of networks and configurations.Accordingly, the illustrations provided herein are not intended to limitthe embodiments of the invention and are merely to aid in thedescription of aspects of embodiments of the invention.

Access terminals can be configured to connect to servers, such as theapplication server 170, through one of a plurality of systems ornetworks. For example, a given access terminal can connect to theapplication server 170 via a WiFi system (e.g., 802.11a/b, etc.), aCDMA2000 1x system, a Wideband CDMA (WCDMA) system, a FDMA system, aTDMA system, a OFDM system, a long-term evolution (LTE) system, a BCMCSsystem by which the RAN 120 transmits messages to multiple ATs within agiven sector on a shared downlink channel, such as a broadcast channel(BCH), a multimedia broadcast/multicast services (MBMS) system and/or aunicast 1x EV-DO system by which the RAN 120 transmits messages to asingle AT on a downlink dedicated channel (DCH) or unicast channel.Accordingly, the term ‘system’ as used herein, in the context ofproviding service to an access terminal through the RAN 120, correspondsto any type of wireless technology through which the access terminal canestablish a link to other network components, such as the applicationserver 170.

The access terminal can setup a communication session (e.g., apush-to-talk (PTT) session, a VoIP session, a half-duplex session, afull-duplex session, etc.) on a first system, and can later switch fromthe first system to a second system without terminating thecommunication session. This type of switch can be referred to as aninter-system handover or handoff. An inter-system handoff of the accessterminal between systems (e.g., EV-DO, 1x, BCMCS, cdma2000 1X, etc.)should not be confused with a handoff of the access terminal from oneserving area (e.g., a cell, sector, subnet, etc.) to another servingarea. In other words, the access terminal can handoff from one type ofsystem providing service to another type of system, and the accessterminal can also (separately) handoff from one service area for aparticular system to another service area for the same system.Embodiments of the invention are generally directed to inter-systemhandoff, although this does not preclude a serving-area handoff fromoccurring in conjunction with the embodiments described herein.

Handoffs of the access terminal from one system (e.g., BCMCS) to anothersystem (e.g., 1x, unicast EV-DO, etc.) are conventionally controlled atthe AT with software that operates at a lower-layer, such as thephysical layer. This software construct may be referred to as a lowerlayer controller, and may be stored in memory 212 and executed by theASIC 208. In an example, the lower layer controller can basehandoff-decisions on physical layer parameters, such as frame-error-rate(FER), pilot signal strength, detection of a new system, etc. Generally,this means the lower layer controller evaluates how well packetscontaining data are exchanged on a packet-by-packet or physicalframe-by-frame basis, without taking into account the higher-level orapplication-layer uses of the actual data. Furthermore, inter-systemhandoff generally requires complex signaling exchanges between the ATand the RAN 120 in order to command the related measurements, report theresults, and transmit handoff commands in a seamless manner.

FIG. 4 illustrates a conventional inter-system handoff of a given accessterminal (“AT 1”) that is participating in a wireless communicationsession. Referring to FIG. 4, assume that AT 1 is configured to connectto the RAN 120 on either a first system or a second system. Forconvenience of explanation, assume that the first system corresponds togenerally to EV-DO and the second system corresponds to BCMCS.

Referring to FIG. 4, AT 1 sets up a communication session on the firstsystem, 400. For example, if the communication session corresponds to aPTT session originated by AT 1, a multimedia client 210A that isresponsible for managing AT 1's PTT session at the application-layerreceives an indication that a user of AT 1 has pushed a PTT button. Themultimedia client 210A then requests the lower layer controller toschedule and send a call message to the application server 170. Afterobtaining or waiting for the requisite call resources, the lower layercontroller sends the call message to the RAN 120 (e.g., on a reverselink access channel or a R-TCH), which is forwarded to the applicationserver 170, which announces the session to one or more target ATs andthen sends a floor-grant to AT 1 after at least one target AT acceptsthe announced session.

While the communication session is conducted on the first system, thelower layer controller monitors one or more lower-layer performanceparameters associated with the communication session, 405. For example,the one or more lower-layer performance parameters may include aframe-error-rate (FER) for packets associated with the communicationsession. Alternatively or additionally, the lower layer controller maymonitor a pilot signal strength of the first system.

Based on the monitored one or more lower-layer performance parameters,the lower layer controller determines whether to trigger a handoff of AT1 from the first system to the second system, 410. For example, if thelower layer controller is configured to make handoff decisions betweensystems for AT 1 based on FER, then the decision of 410 may correspondto comparing a current FER or running-average FER for AT 1'scommunication session on the first system with a threshold FER, and thenselectively triggering a handoff if the current or running-average FERis higher than the threshold FER.

If the lower layer controller of AT 1 determines not to handoff to thesecond system in 410, the process returns to 405 and AT 1 continues tomonitor the one or more lower-layer performance parameters while thecommunication system continues on the first system. Otherwise, if thelower layer controller of AT 1 determines to handoff to the secondsystem in 410, the lower layer controller initiates or triggers thehandoff of AT 1 from the first system to the second system, as is knownin the art, 415. For example, if the first system is BCMCS and thesecond system is unicast EV-DO, then the handoff to the second systemmay include requesting a unicast TCH and de-registering with the RAN 120for multicast support via BCMCS. The particular signaling that occurs tofacilitate the handoff in 415 is not shown because this signaling can bedifferent for handoffs between different systems of the RAN 120 (e.g.,EV-DO to 1x, BCMCS to unicast EV-DO, unicast EV-DO to WiFi, etc.). Aftercompleting the handoff that is initiated in 415, AT 1 continues thecommunication session on the second system, if possible, 420.

It should be noted that many systems do not support inter-system lowerlayer signaling. Even if such systems do, inter-system handoff isconventionally restricted to/from a restricted set of systems. For thesereasons, supporting the inter-system handoff at the lower layer canrequire significant enhancements to the existing systems. On the otherhand, the application-initiated inter-system handoff can be implementedusing existing layer signaling messages without requiring any systemenhancements. Specific mechanisms for initiating the inter-systemhandoff at the application layer will be elaborated later.

As will be appreciated by one of ordinary skill in the art, the processof FIG. 4 can potentially permit AT 1 to handoff to another system withsuperior physical-layer performance characteristics in the event ofphysical-layer performance degradation on a current system. In theabsence of lower layer support, it is possible that the degradedperformance related to the communication session at theapplication-level and the existence of an alternative system can triggeran application-driven inter-system handoff. For example, thecommunication session may undergo a relatively high media-error-rate(MER) and/or outage duration (OD), which occurs at theapplication-level. If the application finds availability of analternative/second system, the application may attempt to handoff to thesecond system. In another example, if an access terminal is supported bya system with a higher charging rate than another available system(e.g., the AT is connected to a cellular network and hands off to aroaming service area, a free WiFi connection becomes available while theAT is connected to an in-network cellular system that is costing a userthereof usage minutes, etc.), the user thereof may wish to handoff tothe cheaper system. Accordingly, embodiments of the invention aregenerally directed to making system handoff decisions based on one ormore application-layer criteria either in place of or in addition tolower-layer (e.g., physical-layer) considerations as in FIG. 4.

FIG. 5 illustrates a system-handoff of a given access terminal (“AT 1”)that is participating in a wireless communication session in accordancewith an embodiment of the invention. In particular, FIG. 5 illustratesthe inventive inter-system handoff process at a relatively high level,with examples of more detailed implementations provided afterwards withrespect to FIGS. 6A through 6E. Referring to FIG. 5, assume that AT 1 isconfigured to connect to the RAN 120 on at least two systems or wirelessconnection technologies (e.g., EV-DO, BCMCS, 1x, WiFi, Bluetooth, etc.).

Referring to FIG. 5, AT 1 sets up a communication session on the firstsystem, 500. For example, if the communication session corresponds to aPTT session originated by AT 1, a multimedia client 210A that isresponsible for managing AT 1's PTT session at the application-layerreceives an indication that a user of AT 1 has pushed a PTT button. Themultimedia client 210A then requests the lower layer controller toschedule and send a call message to the application server 170. Afterobtaining or waiting for the requisite call resources, the lower layercontroller sends the call message to the RAN 120 (e.g., on a reverselink access channel or a R-TCH), which is forwarded to the applicationserver 170, which announces the session to one or more target ATs andthen sends a floor-grant to AT 1 after at least one target AT acceptsthe announced session.

While not illustrated in FIG. 5, while the communication session isconducted on the first system, the lower layer controller can monitorone or more lower-layer performance parameters associated with thecommunication session as in FIG. 4, and the lower layer controller caninitiate handoffs based on the lower-layer or physical-layer performanceof the different systems. However, in FIG. 5, performance at thephysical-layer need not be the only type of performance considered indetermining whether to handoff from one system to another.

Accordingly, the multimedia client 210A measures one or moreapplication-layer performance parameters for the communication systemthat is being supported by the first system of the RAN 120, 505. Forexample, the one or more application-layer performance parameters caninclude (i) a media-error-rate (MER) of the communication session (e.g.,based on a success rate of audio frames if the communication session isan audio session, based on a success rate of video and/or audio framesif the communication session is a video conference), (ii) an outageduration (OD) of the communication session (e.g., a period of downlinkinactivity due to successive media errors on the communication session),(iii) a rate at which the first system is currently charging a user ofAT 1 for usage related to the communication session), (iv) themultimedia client's 210A status as floor-holder or listener if thecommunication corresponds to a half-duplex PTT session, (v) a priorityof the user of AT 1 (e.g., such that a priority of a user of AT 1 isevaluated, and a handoff to a system with superior application-layerperformance is only performed if the user's priority is sufficient topermit using the target system for a current application), and/or (vi)any combination thereof.

Based on the monitored one or more application-layer performanceparameters, the multimedia client 210A determines whether to trigger ahandoff of AT 1 from the first system to the second system, 510. Thedetermination of 510 may not only be based upon the application-layerperformance parameter(s) for the communication session on the firstsystem, but can also be based on the availability of one or more othersystems, an expected application-layer performance of any availablesystems, etc. Examples of the application-layer system handoff decisionblock of 510 are given below with respect to FIGS. 6A through 6E.

If the multimedia client 210A of AT 1 determines not to handoff to thesecond system in 510, the process returns to 505 and AT 1 continues tomonitor the one or more lower-layer performance parameters while thecommunication system continues on the first system. Otherwise, if themultimedia client 210A of AT 1 determines to handoff to the secondsystem in 510, the multimedia client 210A initiates or triggers thehandoff of AT 1 from the first system to the second system, as is knownin the art, 515. In general, the signaling that occurs to facilitate thehandoff in 515 includes releasing the connection with the first systemand establishing the connection with the second system. This is notshown explicitly in FIG. 5 because this signaling can be different fordifferent systems of the RAN 120 (e.g., EV-DO to 1x, BCMCS to unicastEV-DO, unicast EV-DO to WiFi, etc.). After completing the handoff thatis initiated in 515, AT 1 continues the communication session on thesecond system, if possible, 520.

As will be appreciated by one of ordinary skill in the art from a reviewof FIG. 5, the multimedia client 210A has access to higher-levelinformation regarding the communication session as compared to the lowerlayer controller. As such, the multimedia client 210A can potentially bein a better position to evaluate whether a system handoff is called forby taking into account performance of the communication session at theapplication layer, and not merely the physical layer. More detailedimplementation examples of the process of FIG. 5 will now be providedwith respect to FIGS. 6A through 6E.

FIG. 6A illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to a location of AT1 within the wireless communications system 10 in accordance with anembodiment of the invention.

Referring to FIG. 6A, AT 1 sets up a communication session on the firstsystem, 600A, as described above with respect to 500 of FIG. 5. In 605A,the multimedia client 210A determines location information associatedwith AT 1. The location information may correspond to a base stationcurrently serving AT 1, a geographic coordinate of AT 1 (e.g., a GPScoordinate), and/or any other manner of identifying AT 1's location. In610A, the multimedia client 210A compares AT 1's location informationwith a defined location region of the system 10. In an example, thedefined location region corresponds to a list of sectors, such that ifAT 1's current sector from 605A is in the list of sectors the multimediaclient 210A can infer whether a particular system (e.g., unicast EV-DO,BCMCS, etc.) is available and/or permitted for use by AT 1. Definedlocation regions and methodologies for determining location informationis described in more detail within co-pending U.S. Provisional PatentApplication No. 61/163,834, entitled “REGULATING THE SCOPE OF SERVICEGEOGRAPHICALLY IN WIRELESS NETWORKS”, filed on Mar. 26, 2009, assignedto the same assignee of the subject application, and hereby incorporatedby reference in its entirety.

Accordingly, in the example of FIG. 6A, the one or more measuredapplication-layer performance parameters includes some type of locationinformation associated with AT 1. If the location comparison of 610Aindicates that AT 1 is inside of or outside of the defined locationregion, the multimedia client 210A may determine whether to attempt ahandoff to another system. For example, the defined location region mayindicate sectors that are configured to support AT 1's communicationsession on the first system, such that if AT 1 now determines itself tobe outside of the defined location region, the multimedia client 210Aknows that a handoff to another system needs to be made or else thecommunication session is going to be dropped. In another example, thedefined location region may indicate sectors where a more desirablesystem (“second system”) than the first system is available forsupporting AT 1's communication session. In a further example, the firstsystem may correspond to BCMCS for supporting a group communicationsession via IP multicasting protocols within the EV-DO network of theRAN 120, and the second system may correspond to unicast EV-DO forsupporting the group communication session via IP unicasting protocolswithin the EV-DO network of the RAN 120 (or vice versa).

Based on the relationship between AT 1's location information from 605Aand the defined location region, the multimedia client 210A eithercontinues to monitor the location of AT 1 during the communicationsession on the first system and returns to 605A, or else advances to615A. In 615A, AT 1 determines whether a second system is available forsupporting AT 1's communication session with a level ofapplication-layer performance expected to be higher than the firstsystem. In an example, the presence of the second system can be inferredfrom AT 1's relationship to the defined location region. If no secondsystem is determined to be available for supporting AT 1's communicationsession in 615A, the process returns to 605A and AT 1 continues tomonitor AT 1's location during the communication session on the firstsystem. Otherwise, if the second system associated with a higherexpected level of application-layer performance is determined to beavailable in 615A, the multimedia client 210A initiates or triggers thehandoff of AT 1 from the first system to the second system, as is knownin the art, 620A. After completing the handoff that is initiated in620A, AT 1 continues the communication session on the second system, ifpossible, 625A. Accordingly, the embodiment of FIG. 6A illustrates onemanner by which location of an access terminal can be used to determinewhen to perform inter-system handoffs of the access terminal.

Referring to FIG. 6A, each time AT 1 re-determines its location of AT 1in 605A, the decision logic associated with blocks 610A and 615A may useAT 1's newly acquired location to determine whether or not to perform aninter-system handoff. In an example, each iteration of AT 1 determiningits location can be timer-based (i.e., performed at a given period), orevent based, or a combination thereof. In an example, events that maytrigger AT 1 to determine its location may include a media-error-rate(MER) for the communication session on a current system rising above athreshold, when AT 1 hands off to a new cell or sector (e.g., such aswhen a Broadcast Multicast Service (BCMCS) flow status reported by AT 1becoming unavailable as the AT enters a sector that does not broadcastthe desired BCMCS flow) and/or any other potential event that has thepotential to affect system performance and/or availability.

FIG. 6B illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to a media errorrate (MER) for AT 1's communication session within the wirelesscommunications system 10 in accordance with an embodiment of theinvention.

Referring to FIG. 6B, AT 1 sets up a communication session on the firstsystem, 600B, as described above with respect to 500 of FIG. 5. In 605B,the multimedia client 210A monitors the MER for the communicationsession on the first system. For example, the monitored MER maycorrespond to a time-averaged indication of the number of errorsexperienced by the multimedia client 210A. As will be appreciated by oneof ordinary skill in the art, the MER differs from the FER because theFER is measured at the physical-layer, whereas the MER is measured atthe application-layer. Thus, the MER is based on whether errors areexperienced in the actual media being played by the multimedia client210A on AT 1, for example, whereas the FER is based on frame-decodingerrors of individual transport packets.

After determining the MER for the communication session on the firstsystem in 605B, the multimedia client 210A compare AT 1 MER with an MERthreshold, 610B. If AT 1's MER is determined to be lower than the MERthreshold in 610B, the process returns to 605B and the multimedia client210A continues to monitor the MER during the communication session onthe first system. Otherwise, if AT 1's MER is determined to be greaterthan or equal to the MER threshold in 610B, AT 1 determines whether asecond system is available for supporting AT communication session witha level of application-layer performance expected to be higher than thefirst system, 615B. In the example of FIG. 6B, this means a system thatis expected to provide a MER that is lower than the MER threshold, or atleast lower than the MER associated with the first system for AT 1'scommunication session.

If no second system is determined to be available for supporting AT 1'scommunication session in 615B, the process returns to 605B and AT 1continues to monitor the MER during the communication session on thefirst system. Otherwise, if the second system associated with a higherexpected level of application-layer performance is determined to beavailable in 615B, the multimedia client 210A initiates or triggers thehandoff of AT 1 from the first system to the second system, as is knownin the art, 620B. After completing the handoff that is initiated in620B, AT 1 continues the communication session on the second system, ifpossible, 625B. Accordingly, the embodiment of FIG. 6B illustrates onemanner by which MER can be used to determine when to performinter-system handoffs of the access terminal.

FIG. 6C illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to an outageduration for AT 1's communication session within the wirelesscommunications system 10 in accordance with an embodiment of theinvention.

Referring to FIG. 6C, AT 1 sets up a communication session on the firstsystem, 600C, as described above with respect to 500 of FIG. 5. In 605C,the multimedia client 210A monitors the OD for the communication sessionon the first system. For example, the monitored OD may correspond to aperiod during which media associated with the communication session isnot received from the first system of the RAN 120. In a further example,the OD may correspond to a timer that is reset after each successfulapplication-layer media frame is output by multimedia client 210A (e.g.,a video frame, an audio frame, etc.).

After determining the OD for the communication session on the firstsystem in 605C, the multimedia client 210A compare AT 1's OD with an ODthreshold, 610C. If AT 1's OD is determined to be lower than the ODthreshold in 610C, the process returns to 605C and the multimedia client210A continues to monitor the OD during the communication session on thefirst system. Otherwise, if AT 1's OD is determined to be greater thanor equal to the OD threshold in 610C, AT 1 determines whether a secondsystem is available for supporting AT 1's communication session with alevel of application-layer performance expected to be higher than thefirst system, 615C. In the example of FIG. 6C, this means a system thatis expected to provide an OD that is lower than the OD threshold, or atleast lower than the OD associated with the first system for AT 1'scommunication session.

If no second system is determined to be available for supporting AT 1'scommunication session in 615C, the process returns to 605C and AT 1continues to monitor the OD during the communication session on thefirst system. Otherwise, if the second system associated with a higherexpected level of application-layer performance is determined to beavailable in 615C, the multimedia client 210A initiates or triggers thehandoff of AT 1 from the first system to the second system, as is knownin the art, 620C. After completing the handoff that is initiated in620C, AT 1 continues the communication session on the second system, ifpossible, 625C. Accordingly, the embodiment of FIG. 6C illustrates onemanner by which OD can be used to determine when to perform inter-systemhandoffs of the access terminal.

FIG. 6D illustrates the system-handoff process of FIG. 5 whereby oneapplication-layer performance parameter corresponds to a current rate atwhich a subscriber using AT 1 is being charged for service related to AT1's communication session within the wireless communications system 10in accordance with an embodiment of the invention.

Referring to FIG. 6D, AT 1 sets up a communication session on the firstsystem, 600D, as described above with respect to 500 of FIG. 5. In 605D,the multimedia client 210A monitors the current rate at which thesubscriber using AT 1 is being charged for service related for thecommunication session on the first system. For example, if the firstsystem corresponds to the subscriber's home WiFi network which isconfigured to provide unlimited service for a fixed rate, than thecharging rate for AT 1's communication session on the first system maybe interpreted as zero. In another example, if the first systemcorresponds to the subscriber's 1x cellular provider which is configuredto provide a certain number of minutes and afterwards charge afee-per-minute of usage, the charging rate for AT 1's communicationsession on the first system may be interpreted as either a monetaryequivalent of a minute of usage or the fee-per-minute, dependent on howmuch usage the subscriber has incurred. As will be appreciated,different metering plans associated with system-connectivity mean thatthe monitored charging rate of 605D can correspond to any of variousmanners by which subscribers are charged for service.

After determining the charging rate for the communication session on thefirst system in 605D, the multimedia client 210A compare AT 1's chargingrate with a charging rate threshold, 610D. If AT 1's charging rate isdetermined to be lower than the charging rate threshold in 610D, theprocess returns to 605D and the multimedia client 210A continues tomonitor the charging rate during the communication session on the firstsystem. Otherwise, if AT 1's charging rate is determined to be greaterthan or equal to the charging rate threshold in 610D, AT 1 determineswhether a second system is available for supporting AT 1's communicationsession with a level of application-layer performance expected to behigher than the first system, 615D. In the example of FIG. 6D, thismeans a system that is expected to provide a charging rate that is lowerthan the charging rate threshold, or at least lower than the chargingrate associated with the first system for AT 1's communication session.For example, if the second system is a BCMCS system that is broadcastinga certain multicast session that the AT has been monitoring in the firstsystem using a dedicated channel (e.g., in EV-DO or 1x), the chargingrate of the second system will be cheaper. In an example, the chargingrate threshold need not actually be used, and the process of FIG. 6D canrather advance directly to FIG. 6D where AT 1's current charging rate issimply compared against the charging rate(s) of one or more otheravailable systems.

If no second system is determined to be available for supporting AT 1'scommunication session in 615D, the process returns to 605D and AT 1continues to monitor the charging rate during the communication sessionon the first system. Otherwise, if the second system associated with ahigher expected level of application-layer performance is determined tobe available in 615D, the multimedia client 210A initiates or triggersthe handoff of AT 1 from the first system to the second system, as isknown in the art, 620D. After completing the handoff that is initiatedin 620D, AT 1 continues the communication session on the second system,if possible, 625D. Accordingly, the embodiment of FIG. 6D illustratesone manner by which charging rates can be used to determine when toperform inter-system handoffs of the access terminal.

In the embodiments of FIGS. 6A through 6D, handoffs between a firstsystem and a second system are described as being based on differentapplication-layer performance parameters. While each of FIGS. 6A through6D are described with respect to one particular application-layerperformance parameter, it will be appreciated that multipleapplication-layer performance parameters can be considered with regardto any system handoff decision at AT 1. For example, two or more of OD,MER, location and/or a current charging rate may be considered in adecision with regard to whether to handoff to another system, with anetwork operator or user of AT 1 establishing which application-layerperformance parameter has priority over other parameters. Thus, if anyof the designated application-layer performance parameters degradesduring AT 1's communication session, a handoff to another system maypotentially be triggered so long as superior performance is expected atleast with the regard to the degraded parameter (e.g., with at least athreshold amount of performance expected for each other parameter ofequal or higher priority than the degraded parameter).

Further, FIGS. 6A through 6D are each described with respect to twoparticular systems; namely, AT 1's current system (“first system”) and aprospective system (“second system”) under consideration for a potentialhandoff. However, it is possible that multiple systems are available forhandoff from the first system. In this case, each available system maybe evaluated during a handoff decision, as described below with respectto FIG. 6E.

FIG. 6E illustrates the system-handoff process of FIG. 5 whereby one ormore application-layer performance parameters are considered during apotential handoff of AT 1 from a first system (e.g., system 1) to one ofa plurality of other potential systems (e.g., systems 2 . . . N, whereN>2) during AT 1's communication session within the wirelesscommunications system 10 in accordance with an embodiment of theinvention.

Referring to FIG. 6E, AT 1 sets up a communication session on the firstsystem, 600E, as described above with respect to 500 of FIG. 5. In 605E,the multimedia client 210A monitors one or more application-layerperformance parameters for AT 1's communication session on the firstsystem (e.g., OD, MER, charging rate, location, any combination thereof,etc.). After determining or measuring the one or more application-layerperformance parameters for AT 1's communication session on the firstsystem, the multimedia client 210A determines whether the determinedparameters indicate that performance on the first system is sufficientfor AT 1's communication session, 610E. If the first system isdetermined by the multimedia client 210A to provide adequateperformance, the process returns to 605E and AT 1 continues to monitorthe application layer performance parameters while the communicationsession continues on the first system. Otherwise, if the first system isdetermined by the multimedia client 210A not to provide adequateperformance, the multimedia client 210A determines an expectation ofperformance for AT 1's communication session on each of a plurality ofsystems 2 . . . N, 615E. For example, if the application-layerperformance parameters include a charging rate for the communicationsession, the multimedia client 210A can determine how much thesubscriber using AT 1 would be charged on each of systems 2 . . . N. Inanother example, if the application-layer performance parameters includeAT 1's location, the multimedia client 210A can determine which ofsystems 2 . . . n are available and/or a degree of performance based onAT 1's location, and so on.

In 620E, the multimedia client 210A determines a system among systems 2. . . N associated with a highest performance expectation. In anexample, it is possible that a given system among systems 2 . . . N hasa higher performance expectation for one parameter and a lowerperformance expectation for another parameter. In this case, eachperformance parameter can be assigned a weight (e.g., as in an objectivefunction) and a combined performance valuation can be computed, with thehighest combined performance valuation corresponding to the system thatis, overall, expected to provide a highest level of performance.

Next, in 625E, the multimedia client 210A determines whether thehighest-rated system from 620E is expected to provide better performancethan the first system that AT 1 is currently using for support of itscommunication session. If the highest-rated system among systems 2 . . .N is not expected to provide better performance than the first system,the process returns to 605E and AT 1 continues to monitor theapplication layer performance parameters while the communication sessioncontinues on the first system. Otherwise, if the highest-rated systemamong systems 2 . . . N is expected to provide better performance thanthe first system, the multimedia client 210A initiates or triggers thehandoff of AT 1 from the first system to the highest-rated system amongsystems 2 . . . N, as is known in the art, 630E. After completing thehandoff that is initiated in 630E, AT 1 continues the communicationsession on its new system, if possible, 635E.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods, sequences and/or algorithms described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal (e.g., access terminal). Inthe alternative, the processor and the storage medium may reside asdiscrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

While the foregoing disclosure shows illustrative embodiments of theinvention, it should be noted that various changes and modificationscould be made herein without departing from the scope of the inventionas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the embodiments of the inventiondescribed herein need not be performed in any particular order.Furthermore, although elements of the invention may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

1. A method of participating in a communication session within acommunications system, comprising: participating in a communicationsession supported over a first system associated with a first physicallayer; monitoring one or more application-layer performance parametersassociated with the communication session; determining, based at leastin part on the monitoring step, whether to hand off the communicationsession from the first system to a second system associated with asecond physical layer; and selectively handing off the communicationsession from the first system to the second system based on thedetermining step.
 2. The method of claim 1, wherein the first systemand/or the second system corresponds to one or more of a WiFi system, aCDMA2000 1x system, a Wideband CDMA (WCDMA) system, a frequency divisionmultiple access (FDMA) system, a time division multiple access (TDMA)system, a orthogonal frequency division multiplexing (OFDM) system, along-term evolution (LTE) system, a broadcast and multicast service(BCMCS) system and/or a multimedia broadcast/multicast services (MBMS)system.
 3. The method of claim 1, wherein the one or moreapplication-layer performance parameters include whether a location ofan access terminal (AT) satisfies a given relationship with respect to adefined location region, a media error rate (MER) of the communicationsession supported over the first system, an outage duration (OD) of thecommunication session supported over the first system and/or a chargingrate associated with the communication session supported over the firstsystem.
 4. The method of claim 1, wherein the determining stepdetermines to hand off the communication session from the first systemto the second system based in part on the monitoring step and also basedin part on an availability and/or application-layer performanceexpectation of the second system in the event of a handoff.
 5. Themethod of claim 1, wherein the first and/or second systems supportingthe communication session correspond to different connection mechanismsof an access network through which an access terminal (AT) participatingin the communication session communicates with an application serverthat is arbitrating the communication session between the AT and atleast one other AT.
 6. The method of claim 1, wherein the one or moreapplication-layer performance parameters includes whether a location ofan access terminal (AT) satisfies a given relationship with respect to adefined location region.
 7. The method of claim 6, wherein themonitoring step includes: determining the location of the AT; comparingthe determined location of the AT with the defined location region, thedefined location region defining an area where the first system cansupport the communication session; and attempting a handoff of thecommunication session from the first system to the second system if thecomparison indicates that the determined location of the AT is not in anarea where the first system can support the communication session. 8.The method of claim 7, wherein the attempting step is only performed ifthe second system is determined to be available for a handoff.
 9. Themethod of claim 8, wherein the attempting step is only performed if anapplication-layer performance expectation of the second system is abovea performance threshold.
 10. The method of claim 7, wherein theattempting step is only performed if a priority of a user of the accessterminal (AT) is sufficient to permit using the second system for thecommunication session.
 11. The method of claim 1, wherein the one ormore application-layer performance parameters includes a media errorrate (MER) of the communication session supported over the first system.12. The method of claim 11, wherein the monitoring step includes:determining the MER during at least a portion of the communicationsession supported over the first system; comparing the determined MERwith a MER threshold; and attempting a handoff of the communicationsession from the first system to the second system if the comparisonindicates that the determined MER is above the MER threshold.
 13. Themethod of claim 12, wherein the attempting step is only performed if thesecond system is determined to be available for a handoff.
 14. Themethod of claim 13, wherein the attempting step is only performed if anapplication-layer performance expectation of the second system is abovea performance threshold.
 15. The method of claim 11, wherein theattempting step is only performed if a priority of a user of the accessterminal (AT) is sufficient to permit using the second system for thecommunication session.
 16. The method of claim 1, wherein the one ormore application-layer performance parameters includes an outageduration (OD) of the communication session supported over the firstsystem.
 17. The method of claim 16, wherein the monitoring stepincludes: determining the OD during at least a portion of thecommunication session supported over the first system; comparing thedetermined OD with an OD threshold; and attempting a handoff of thecommunication session from the first system to the second system if thecomparison indicates that the determined OD is above the OD threshold.18. The method of claim 17, wherein the attempting step is onlyperformed if the second system is determined to be available for ahandoff.
 19. The method of claim 18, wherein the attempting step is onlyperformed if an application-layer performance expectation of the secondsystem is above a performance threshold.
 20. The method of claim 17,wherein the attempting step is only performed if a priority of a user ofthe access terminal (AT) is sufficient to permit using the second systemfor the communication session.
 21. The method of claim 1, wherein theone or more application-layer performance parameters includes a chargingrate of the communication session supported over the first system. 22.The method of claim 21, wherein the monitoring step includes:determining the charging rate during at least a portion of thecommunication session supported over the first system; comparing thedetermined charging rate with a charging rate threshold; and attemptinga handoff of the communication session from the first system to thesecond system if the comparison indicates that the determined chargingis above the charging rate threshold.
 23. The method of claim 21,wherein the attempting step is only performed if the second system isdetermined to be available for a handoff.
 24. The method of claim 22,wherein the charging rate threshold corresponds to a charging rateassociated with conducting the communication session over the secondsystem.
 25. The method of claim 21, wherein the attempting step is onlyperformed if a priority of a user of the access terminal (AT) issufficient to permit using the second system for the communicationsession.
 26. The method of claim 1, wherein the determining stepincludes: if the monitoring step indicates that the one or moreapplication-layer performance parameters are not sufficient, evaluatingapplication-layer performance expectations associated with conductingthe communication system on each of a plurality of systems other thanthe first system; and if the evaluating step indicates at least one ofthe plurality of systems is expected to provide better application-layerperformance than the first system, selecting one of the plurality ofsystems as the second system.
 27. The method of claim 1, wherein theselected system corresponds to a given system amount the plurality ofsystem having the highest application-layer performance expectation. 28.An access terminal configured to participate in a communication sessionwithin a communications system, comprising: means for participating in acommunication session supported over a first system associated with afirst physical layer; means for monitoring one or more application-layerperformance parameters associated with the communication session; meansfor determining, based at least in part on the monitoring, whether tohand off the communication session from the first system to a secondsystem associated with a second physical layer; and means forselectively handing off the communication session from the first systemto the second system based on the determination.
 29. An access terminalconfigured to participate in a communication session within acommunications system, comprising: logic configured to participate in acommunication session supported over a first system associated with afirst physical layer; logic configured to monitor one or moreapplication-layer performance parameters associated with thecommunication session; logic configured to determine, based at least inpart on the monitoring, whether to hand off the communication sessionfrom the first system to a second system associated with a secondphysical layer; and logic configured to selectively hand off thecommunication session from the first system to the second system basedon the determination.
 30. A computer-readable storage medium comprisingprogram code, which, when executed by an access terminal configured toparticipate in a communication session within a communications system,causes the access terminal to perform operations, the program codecomprising: program code to participate in a communication sessionsupported over a first system associated with a first physical layer;program code to monitor one or more application-layer performanceparameters associated with the communication session; program code todetermine, based at least in part on the monitoring, whether to hand offthe communication session from the first system to a second systemassociated with a second physical layer; and program code to selectivelyhand off the communication session from the first system to the secondsystem based on the determination.